The death or damage of neurons is a hallmark of neurodegenerative illnesses and disorders, including, for example, dementia, Alzheimer's, Huntington's, and Parkinson's disease. Parkinson's disease (PD) affects more than 1% of the population over the age of 60 in the U.S. (Allam et al., 2005; West et al., 2005). PD is believed to be caused by lack of the neurotransmitter, dopamine, in the basal ganglia of the brain. In large part, this dopamine deficiency is attributed to the degeneration of nigral dopaminergic neurons. (Przedborski, 2005). Both clinical and experimental evidence clearly demonstrates that oxidative stress and apoptosis are key cellular mechanisms that contribute to the neuronal loss (Maguire-Zeiss et al., 2005). There is no cure for PD. Treatments available at present only target symptoms of the disease. In light of the selective death of dopamine producing neurons, administration of L-dihydroxyphenylalanine (L-DOPA) remains the most widely used treatment of Parkinson's disease. However, L-dopa has limited and transient efficacy.
Current approaches fail to prevent the progression of the neurodegenerative process and sustain or increase dopamine levels. Although the pathology and clinical symptoms are well defined in PD, the cellular and molecular mechanisms underlying the selective degeneration of dopaminergic neurons still remains elusive.
Protein kinase C (PKC) belongs to a family of serine threonine protein kinases. To date, twelve isoforms in the PKC subfamily have been identified. Kanthasamy et al., 2003; Antioxidants & Redox Signaling, 5: 609-620. One such isoform is protein kinase C delta (PKCδ). Martelli A M, Mazzotti G, Capitani S, Nuclear protein kinase C isoforms and apoptosis. Eur J Histochem. 2004; 48(1):89-94.
PKCd was originally discovered by Gschwendt et al. in 1986, Gschwendt M, Kittstein W, and Marks F. A novel type of phorbol ester-dependent protein phosphorylation in the particulate fraction of mouse epidermis. Biochem Biophys Res Commun. 137: 766-74, 1986., and cloned from a rat brain cDNA library the following year. Kurkinen K M, Keinanen R A, Karhu R, and Koistinaho J. Genomic structure and chromosomal localization of the rat protein kinase Cdelta-gene. Gene 242: 115-23, 2000., Ono Y, Fujii T, Ogita K, Kikkawa U, Igarashi K, and Nishizuka Y. Identification of three additional members of rat protein kinase C family: delta-, epsilon- and zeta-subspecies. FEBS Lett. 226: 125-8, 1987. The PKCδ gene is localized on human chromosome 3, Huppi K, Siwarski D, Goodnight J, and Mischak H. Assignment of the protein kinase C delta polypeptide gene (PRKCD) to human chromosome 3 and mouse chromosome 14. Genomics 19: 161-2., 1994, rat chromosome 16, Kurkinen K M, Keinanen R A, Karhu R, and Koistinaho J. Genomic structure and chromosomal localization of the rat protein kinase Cdelta-gene. Gene 242: 115-23, 2000, and mouse chromosome 14, Huppi K, Siwarski D, Goodnight J, and Mischak H. Assignment of the protein kinase C delta polypeptide gene (PRKCD) to human chromosome 3 and mouse chromosome 14. Genomics. 19: 161-2., 1994. There exists a substantial body of evidence that indicates that PKCδ plays a fundamental role in apoptosis. PKCδ has been shown to accumulate in the nucleus of C5 cells, in response to etoposide treatment. Martelli A M, Mazzotti G, Capitani S. Nuclear protein kinase C isoforms and apoptosis. Eur J Histochem. 2004; 48(1):89-94. Overexpression of PKCδ-catalytic fragment results in nuclear localization of the PKCδ fragment and apoptosis. Martelli A M, Mazzotti G, Capitani S. Nuclear protein kinase C isoforms and apoptosis. Eur J Histochem. 2004; 48(1):89-94
Recently, it was reported by the inventors that proteolytic activation of PKCd, a member of the novel PKC isoform family, plays a key role in apoptotic cell death of dopaminergic neurons in a cell culture model of PD as well as oxidative stress models (Anantharam et al., 2002; Kaul et al., 2003; Kitazawa et al., 2003; Yang et al., 2004; Latchoumycandane et al., 2005). It is believed that active PKCd binds to the carboxyl-terminus of DNA-dependent protein kinase (DNA-PK), an enzyme involved in the repair of DNA strand breaks. Once bound, the active PKCd binds to and phosphorylates the DNA-PK. Consequently, the DNA-PK dissociates from the DNA, impedes the repair of DNA strand breaks, and results in DNA fragmentation, one of the hallmarks of apoptosis. It was demonstrated that blockade of PKCd activation by the kinase dominant negative mutant, cleavage-resistant mutant or siRNA almost completely prevented the nigral cell death (Kaul et al., 2003; Kitazawa et al., 2003; Anantharam et al., 2004; Yang et al., 2004; Latchoumycandane et al., 2005).